NA-DEPENDENT GLUTAMINE TRANSPORT IN THE LIVER OF TUMOR-BEARING RATS()

In rats with advanced malignant disease, the liver extracted circulati ng glutamine at a ratio three times faster than the liver of control n on-tumour-bearing animals. This augmented uptake occurred in spite of a fall in circulating glutamine levels, implying an increase in hepato cyte plasma membrane transport. Na+-dependent glutamine transport acti vity (System N) was increased nearly two-fold in hepatocyte plasma mem brane vesicles from tumour-bearing rats; this increase in System N act ivity was proportional to tumour size and was due to an increase in ca rrier V(max) with no change in carrier affinity. Measurement of System N activity in isolated hepatocytes incubated with serum from tumour-b earing rats demonstrated a significant increase in glutamine transport compared with cells incubated with serum from control rats. These dat a indicate that the liver of rats with advanced malignant disease disp lays accelerated glutamine consumption. This increased uptake is due, in part, to enhanced carrier-mediated transport activity, and is media ted by a circulating factor(s) that is not present (or inactive) in no n-tumour-bearing controls.